The present invention relates to a cord-type gas generator that comprises a solid propellant strand that is disposed in a sleeve and comprises a gas-generating material, with the gas generator also comprising an ignition means, whereby the solid propellant strand is disposed in the sleeve in such a way that channels are formed that extend between the sleeve and the solid propellant strand and that are suitable for the formation of an ignition shock wave.
A cord-type gas generator having the aforementioned features is described in DE 39 32 576 C2. The known cord-type gas generator comprises a solid propellant strand having a star-shaped arrangement of individual strands, which are surrounded by a sleeve. Formed between the solid propellant strand and the sleeve are channels in which an ignition shock wave, which is established upon ignition of the solid propellant strand, can expand along the cord-type gas generator. The outer side of the solid propellant strand, which comprises a mixture of binder, perchlorate as well as, if necessary, nitrate, is provided with a coating of explosive that serves as an ignition means and that is ignited via an ignition pulse. The ignition shock wave that results during combustion of the fuel then takes care of the ignition of the solid propellant strand over the entire length thereof.
The known cord-type generator has the drawback that the combustion of the solid propellant takes place too slowly. A further drawback is that the explosive coating of the solid propellant strand makes it difficult, for safety reasons, to use the cord-type gas generator in safety systems of motor vehicles.
It is therefore an object of the present invention to increase the rate of combustion of a cord-type gas generator having the aforementioned features.
This object, including advantageous configurations and embodiments, is realized from the content of the patent claims that follow this specification.
The basic concept of the present invention is that the solid propellant strand, in order to reduce its combustion time, is provided with a reduced woven or material thickness that is established by introducing gaps in the material. To the extent that, as the woven thickness, there is defined the material thickness of the compact strand, which is determined in the cross-section of the solid propellant strand, a reduced material thickness is inventively established in that gaps in the material are introduced into the solid propellant strand, with these gaps dividing the known, compact solid propellant strand, so that the combustion time of the solid propellant strand is reduced.
Pursuant to specific embodiments of the present invention, these gaps in the material are produced by the formation of pores or voids, or by separately introduced interruptions, for example in the form of slits.
To the extent that it is known from the aforementioned DE 39 32 576 C2 for the solid propellant strand to be composed of a plurality of individual arms, it is provided pursuant to one embodiment of the present invention that the individual arms have differing thicknesses, or in addition or alternatively thereto, also have a differing composition of the solid propellant. In this way, the individual arms of the cord-type gas generator can generate gas over different lengths of time, so that, when using the cord-type gas generator for inflating an air bag, the air bag on the one hand reacts rapidly, but at the same time is inflated more gently.
This objective can also be realized by forming the solid propellant strand in the shape of individual strands that are separated from one another and that pursuant to specific embodiments of the invention can have a circular or also a ring-shaped cross-section. In particular, also provided is a combination of different cross-sections of the individual strands that are disposed in a sleeve. Just as with the individual arms, the individual strands can also respectively have a different material thickness, or in addition or alternatively thereto, can also have a different composition of the solid propellant.
To avoid the use of explosive, it is provided pursuant to one specific embodiment that as an ignition means a pyrotechnical mixture be used that in particular is produced on the base of boron, KNO3 and aluminum. This pyrotechnical mixture can be disposed on the outer side of the solid propellant strand, or alternatively or in addition thereto on the inner side of the sleeve that encircles the solid propellant strand. Depending upon the manufacture or consistency of the pyrotechnical mixture, the mixture can be disposed in dry powder form on the solid propellant stand and/or on the sleeve, or can also be applied as a dryable slurry.
With regard to the formation of the solid propellant strand, and the sleeve that encircles the individual strands thereof, the sleeve, as is already known from the aforementioned DE 39 32 576 C2, can comprise a material that burns along with the combustion of the solid propellant stand. Alternatively, the sleeve can comprise a reinforced woven material that either rips open during combustion of the solid propellant strand due to the resulting gas pressure, or that is provided with openings for the passage of the gases generated during the combustion of the solid propellant strand.